The present invention relates to a control device for controlling the level of a liquid in a container, especially in containers in which it is difficult to observe the level of liquid therein. Control devices for this purpose are known in the art, but one disadvantage of such known control devices is that they can be used only for establishing or controlling a fixed predetermined liquid level in the container.
In many applications, it is however, advantageous to vary the maximum level of a liquid in a container, for instance in a screen printing machine in which it is desired to maintain to one side of a squeegee which engages the inner surface of the screen drum of the printing machine a higher or lower pool of paint so as to control the amount of paint passing per time unit through the screen drum. Evidently, by varying the height of the paint pool maintained in the drum, the amount of paint passing through the screen drum per time unit may be accordingly varied.
For instance, during printing of crepe in such a screen printing machine more paint will be needed than during printing of smooth satin or the like.
Also in other applications, for instance, in the chemical industry, control of the liquid level in a container will be necessary, however, the control devices so far known in the art are not adapted to control the liquid level in a container at varying elevations.